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Am Sonntag, 26. August 2012, 14:49:08 schrieb Alex Schuster: |
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> Volker Armin Hemmann writes: |
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> > Am Sonntag, 26. August 2012, 13:41:09 schrieb Alex Schuster: |
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> >> Frank Steinmetzger writes: |
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> >>> Unless the filesystem knows this and starts bigger files at those 512 k |
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> >>> boundaries (so really only one erase cycle is needed for files <=512 k), |
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> >>> isn't this fairly superfluous? |
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> >> |
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> >> Yes, I think it is. When you search for SSD alignment, you read about |
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> >> this alignment all the time, even on the German Wikipedia, and many |
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> >> resources say that this can have a big impact on performance. But I |
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> >> could not find a real explanation at all. |
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> >> |
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> >> Besides that, it's not so easy to do the alignment, at least when using |
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> >> LVM. I read that LVM adds 192K header information, so even if you align |
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> >> the partition start to an erasable block size of 512K, the actual |
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> >> content is not aligned. See [*] for information how to overcome this. |
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> >> That is, if you believe the alignment to erasable blocks is important, |
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> >> personally I do not know what to think now. It wouldn't hurt, so why not |
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> >> apply it, but it seems like snake oil to me now. |
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> >> |
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> >> Wonko |
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> >> |
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> >> http://tytso.livejournal.com/2009/02/20/ |
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> > |
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> > because erasing is slow. You can not overwrite data on a ssd. you have to |
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> > erase first, then reprogramm. Also, erasing shortens lifetime. |
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> |
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> Yes, I know that. But why exactly does it help to align a partition to |
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> the erasable block size? I don't get it. Why isn't it sufficient to |
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> align to the usual 4K block size, so that a block never spans over two |
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> erasable blocks? |
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well, for one, there are lots of ssd which have 8k pages. Not 4k. |
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#163933 |
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